1. Field of the Invention
The present invention relates to an automatic molding system using multiple mold sets. More particularly, the invention concerns the circulation of successive units of stacked mold sets through a repeating molding cycle.
2. Description of Related Art
Prior art molding systems which are related to the invention have been basically controlled by hand and lever mechanisms. Such systems utilize mold cavities which are fixed in a mold container which, in turn, is fixed upon a mold base. The mold base is subsequently attached to a press. The mold cavities are usually arranged in a single layer on the press.
During the molding step, the mold cavities are clamped together in the press and they remain clamped until the injected plastic is initially set. When the press is loosened, the molds are opened and the molded products are removed by lever mechanisms. Subsequently, another group of levers reach into the molds for cleaning.
Mechanical levers are required because the molds remain fixed in the press. If the molded product incorporates a preform, a third group of levers will be needed to position the preform in the mold cavity. Thereafter, a new cycle is started.
The above described system is deficient for the following reasons:
1. Since only a single layer of mold cavities is possible, small increases in production require a large increase in press power.
2. Due to the relatively large surface area covered by the single layer molds, heat losses are excessive. As such, electrical energy requirements are extraordinarily high, not only for heating the molds, but for maintaining them at the required production temperature.
3. Because the press cannot be loosened until the plastic is cooled, the production cycle takes a longer time. Thus, fewer products can be molded per cycle.
4. Because the molds cannot be completely moved out of the press, the cleaning work is difficult. If any flashing or defective moldings become lodged in the mold, the entire mold must be removed from the press.
5. The mechanical levers are complex, difficult to maintain and very expensive to purchase.
6. Because each part of the mold must be exactly coordinated and tightly fixed on the press, it is laborious and time-consuming to change molds. As such, changes are avoided and the overall system is mostly used to produce only one kind of product.
7. Since production levels are limited by the number of mold cavities which, in turn, is limited by area constraints due to the single layer format, only a limited number of products can be produced per cycle.
8. The overall prior art system is cumbersome, heavy, complex and difficult to maintain. It is not readily adaptable to effective automation.